1. Field of the Invention
The invention relates in general to methods and devices for disinfecting and dehumidifying hearing aids, and, more particularly, embodiments of the present invention relate to electrolytic drying and ozone generating methods and devices for sterilizing and dehumidifying hearing aids.
2. Description of the Prior Art
It is well known that hearing aids accumulate water and become biologically contaminated with use. The water is detrimental to the electronic components of the hearing aid. The biological contamination is detrimental to the wearer of the hearing aid. Audio quality is seriously impaired if a hearing aid is humid and contaminated. Previous proposals for dealing with these problems include Schumaier U.S. Pat. No. 5,852,879. Schumaier proposes to dry hearing aids by placing them in a sealed chamber together with a regeneratable desiccant such as silica gel. He further proposes to sterilize the hearing aids with a germicidal lamp that emits radiation in the UV region. Schumaier states that when a UV lamp is used ozone is produced. This ozone is said to act as a deodorizer while the direct radiation kills the bacteria. The need to frequently regenerate or replace the desiccant limits the utility of this proposed system. Treatment with UV radiation is a line of sight process. Areas that are shaded from direct exposure to the UV radiation do not receive treatment. Reliance on UV radiation for germicidal treatment requires physically turning the hearing aid so as to expose all of its surfaces to direct UV radiation. In addition, spaces within the hearing aid are not accessed by the UV radiation and thus are not sterilized. Further, the teaching that a germicidal UV lamp will generate ozone is not clear. Germicidal lamps typically produce ultraviolet light in a narrow spectral band centered at 254 nanometers. It is known that ozone is not generated at this frequency. In fact, Ozone is actually destroyed by ultraviolet light at 254 nanometers. Ozone is generated at an ultraviolet frequency of from about 100 to 200 nanometers, and particularly, 185 nanometers. Ultraviolet at 185 nanometers is not produced by germicidal UV lamps. See Sauska et al., U.S. Pat. No. 6,824,693, and Barnes, U.S. Pat. No. 6,893,610. See also Ted Rich; “A Basic Comparison of Ozone Technologies”, Water Technology Magazine, October 1994. As germicidal UV lamps do not generate ozone, Schumaier's invention, by definition, is not capable of sterilizing a hearing aid by generation of and exposure to ozone.
These and other limitations seriously impair the utility of the previously proposed expedients.
U.S. Pat. No. 5,640,783, also to Schumaier, discloses a dryer appliance for demoisturizing a moisture sensitive item such as an electronic hearing aid or the like, having a housing with a removable cap for providing a substantially sealed chamber and access thereto, a desiccant component mounted in the housing and substantially dividing the chamber into first and second regions, a support in the chamber for supporting at least one item within the first region, one or more passages interconnecting the first and second regions for providing a gas flow circulation path therethrough, the circulation path being (a) gas flow into contact with and through the desiccant component, (b) then into and thru the first region for contact with the item, (c) then thru the passage into the second region, and (d) then again into contact with the desiccant component to continue the circulation, and a gas moving mechanism in the chamber for forcing and maintaining the gas flow circulation path.
The Schumaier invention is sold commercially under the name Dry and Store® and is available from Dry & Store, P.O. Box 1017, Johnson City, Tenn. 37605.
The electrochemical generation of ozone by the electrolysis of water is well known. See, for example, Murphy, U.S. Pat. No. 5,460,705, and Foller et al., U.S. Pat. No. 4,316,782. The efficiency of ozone generation may be increased by the proper selection of electrode material and electrolyte.
U.S. Pat. No. 4,316,782 (Foller) teaches that ozone yields as high as 52% could be obtained where the electrolyte is water and either the acid or salt form of highly electronegative anions, such as hexafluouro-anions are used. Here, the term “fluoro-anions” is used to describe that family of anionic (negatively charged) species in which multiple fluorine ligands complex a central atom. Electrolysis was carried out in a range between room temperature and the freezing point of water. The preferred anode materials for use in the electrolytic cells are either platinum or lead dioxide, especially lead dioxide in the beta crystalline form. Platinum, carbon, or nickel and its alloys may be used as hydrogen-evolving cathodes. Alternatively, an air or oxygen depolarized cathode may be employed which would greatly reduce the cell voltage and enhance the overall energy efficiency of the process.
Such electrolytic solutions can be highly corrosive to the cell materials if they are not selected properly, and especially hard on the electrodes where electrochemical discharge takes place. In addition, the liberated O3, being a powerful oxidizing agent, also strongly acts upon electrode materials which are susceptible to oxidizing action. The electrical properties of the electrode material are also important to the successful and effective operation of the ozone generating electrolytic cell. The electrodes must exhibit sufficient electrical conductivity to enable the utilization of current densities required by the ozone generating process without an unacceptable anode potential and must also be adaptable to whatever cooling procedures are required to maintain cell temperatures during operation.
Foller also disclosed that using an air or oxygen depolarized cathode provided several advantages. (1) The cell voltage would be substantially reduced since replacing hydrogen evolution with the reduction of oxygen theoretically saves 1.23 volts. (In actual practice, a 0.8 volt swing is likely to be achieved.) (2) A separator between anode and cathode is no longer required, as no hydrogen is evolved to depolarize the anode. Further, savings in cell voltage are obtained by reducing IR losses. (3) The overall cell process becomes oxygen in and ozone out and the need for periodic additions of water is reduced. (4) The same air or oxygen fed to the air cathode could also serve to dilute and carry off the ozone that is anodically evolved by flowing through the cathode.
Air cathode technology has found recent favor in its application to fuel cells, metal-air batteries, and the chlor-alkali industry. The electrodes are generally composed of Teflon-bonded carbon containing small amounts of catalytic materials.
U.S. Pat. No. 4,375,395 (Foller) teaches that anodes made of glassy carbon are suitable for use in the preparation of ozone in an electrolytic cell utilizing an aqueous solution of the highly electronegative, fluoro-anions.
U.S. Pat. No. 4,541,989 (Foller) teaches that a liquid electrolyte containing acids of fluoro-anions, such as HBF4 and HPF6, used in combination with a cool electrolyte solution can increase the efficiency and the ozone to oxygen yield. However, the use of a liquid electrolyte causes some problems. First, the electrodes in such electrolytic cell must be separated by a given distance to provide definition. This translates into power loss in the production of heat. Secondly, the presence of liquid electrolytes requires a sophisticated system of seals to prevent leaking of the electrolyte.
U.S. Pat. No. 4,836,929 (Laumnn et al.) teaches the use of a solid electrolyte such as that made by duPont and sold under the brand “NAFION”. This solid electrolyte was placed between a lead dioxide anode and a platinum black cathode. The current efficiency was increased by oxygenating a water stream fed to the anode and the cathode. In this manner, oxygen could be reduced to water at room temperature releasing an increased yield of ozone.
In his paper entitled “Synthesis of Hydrogen Peroxide in a Proton Exchange Membrane Electrochemical Reactor” (April 1993), Fenton disclosed that paired synthesis of ozone (O3) and hydrogen peroxide (H2O2) could be carried out in the same reactor. The electrochemical reactor used a membrane and electrode assembly (M&E) comprised of a “NAFION” 117 membrane between the platinum black/polytetrafluoroethylene (PTFE) anode and graphite/PTFE cathode. This M&E assembly was sandwiched between a carbon fiber paper (Toray Industries) on the cathode side and a platinum mesh (52 mesh, Fisher Scientific) on the anode side, which were used as current collectors. This arrangement was alleged to produce some hydrogen peroxide.
Increasing the percentage of PTFE in the electrode increases the hydrophobicity of the electrode assembly and thus allows more of the gaseous reactant to reach the electrode surface by repelling the products formed. The graphite M&E with 20% PTFE produced slightly higher hydrogen peroxide than a similar M&E with 10% PTFE. This could be due to the mass transport limitation of oxygen to the membrane and electrode assembly within the less hydrophobic 10% M&E. It is preferred that the PEM reactor operate at potentials greater than 3.0 volts where the anodic evolution of ozone is favored.
Membranes containing perfluorinated sulphonic acids are typically prepared before use in an electrochemical cell by first soaking the membrane in hot water for about 30 minutes and then soaking it in 10% HCl to ensure that the entire membrane is in the H.sup.+ form. The membrane has to be kept moist at all times as it acts as a conductor only when it is wet. It is preferred that the proton exchange membrane be pretreated with an aqueous solution of sulphuric acid followed by rinsing the proton exchange membrane with pure water, rinsing the proton exchange membrane with an aqueous solution of hydrogen peroxide, and rinsing the proton exchange membrane with a final rinse of pure water. The final rinse should be made at a temperature between 50° C. and 150° C. and under pressure.
In their paper entitled “Paired Synthesis of Ozone and Hydrogen Peroxide in an Electrochemical Reactor,” Pallav Tatapudi and James Fenton explain that the benefits of paired synthesis in electrolyte free water include: (1) lower energy consumption costs, as two oxidizing agents can be obtained for the price of one; (2) the elimination of the need for transportation and storage of oxidants by generating them electrochemically within water on demand at an amount proportional to the waste concentration; and (3) higher aqueous phase ozone concentrations.
U.S. Pat. No. 4,416,747 (Menth et al.) discloses an individual electrolysis cell bounded by bipolar plates and having a solid electrolyte made of perfluorinated sulphonic acids (“NAFION” by duPont) with a surface coating centrally located between current-collectors and adjoining open metallic structures. A plurality of individual cells may be integrated together between end plates so that the cells are electrically connected in series, hydrodynamically connected in parallel, and combined to form a block.
The current collectors disclosed in Menth may be close-meshed expanded metal covered by an open structure having a low resistance to the flow of a liquid in the direction parallel to the planar structure. The current collectors are preferably made from titanium. The ends of the cell are formed, in each case, by a bipolar plate, which alternately acts as a cathode and as an anode. The bipolar plate is preferably made from stainless (Cr/Ni) steel. The space or chamber between the bipolar plates and the solid electrolyte is completely filled with water in which air or oxygen is suspended and/or dissolved.
The Menth assembly of the electrolysis cells basically corresponds to the filter-press type, with the liquid passing parallel to the principal planes of the cells instead of perpendicularly. The individual cells are held together between two end plates having electrical terminals, thereon.
The method and apparatus disclosed in Menth, however, can support only limited current density associated with reduction-oxidation, since oxygen has only limited solubility in water. Further, since the cathode chamber is filled with liquid water, the cathode electrode structure will become flooded with water. Higher current densities are desirable to cause an increase in the ozone production efficiency.
U.S. Pat. No. 4,836,949 (Laumann et al.) teaches a process for breaking down organic substances and/or microbes in pretreated feed water for high-purity recirculation systems using ozone which is generated in the anode chamber of an electrochemical cell and treated with ultraviolet rays and/or with hydrogen generated in the cathode chamber of the same cell or supplied from outside.
In light of the foregoing discussion, there exists a need for an economical method of producing ozone, which will minimize voltage allowed for higher current density and produce a high concentration of ozone.
The use of ozone in medical sterilization equipment in relatively high concentrations and/or high humidity environments is known. See, for example, Nagashima, U.S. Pat. No. 5,141,722, Faddis et al., U.S. Pat. No. 5,344,622, and Karlson, U.S. Pat. No. 5,868,999. These proposed systems are not suitable for home use because of the safety hazards they pose in the hands of inexperienced or inattentive operators.
The electrolytic drying of small enclosed volumes of air is known. See, for example, Hirschfield, U.S. Pat. No. 4,528,078, Suzuki et al., U.S. Pat. No. 6,547,953, Yamauchi et al., U.S. Pat. No. 5,059,291, and Bredeweg, U.S. Pat. No. 4,050,995. In such systems, generally the water vapor in the enclosure is disassociated by electrolysis into hydrogen and oxygen, but not ozone. Such systems had been proposed for use, for example, in magnetic disk drives, cameras, and electronic instrument packages.
There are numerous deficiencies with the prior art, particularly the Dry & Store®. Use of desiccant for dehumidification is inefficient. This is because the desiccant becomes wetter over time, whether it is used for dehumidification of a hearing aid or not. The desiccant is bulky and must be periodically replaced. Near the end of its dehumidification life it will not dehumidify the hearing aid to the same level of dryness.
As pointed out above, UV irradiation only works line of sight. Sterilization only occurs on surfaces that are directly irradiated by the UV light. All other areas (e.g., the underside, the sound tube, and internal components and compartments of the hearing aid) are not sterilized, but in effect are breading grounds for bacteria, molds, parasites and viruses. Further, partial or incomplete sterilization with time facilitates the evolution of highly resistant and virulent strains of such microorganisms. Moreover, as UV irradiation is a known mutagen, the use of UV irradiation increases mutagenesis within the microorganism residents of the hearing aid, which in turn increases the probability that new and more virulent stains of these microorganisms will develop on, and within the hearing aid.
It is well known that certain strains of bacteria and molds will attack and compromise various components contained within an electrical device and circuit. These components include insulation on wires, and PCB traces, PCB substrates, transducer membranes and cones, semiconductor surfaces such as those used in potentiometers (used for volume control in a variety of hearing aids), metallic contacts and fixtures, plastic components, etc. Thus the incomplete sterilization provided by the present art is non optimal and can in fact exacerbate the attack and subsequent failure of the internal components of the hearing aid.
Moreover, UV irradiation degrades the plastic body of the hearing aid and also any illuminated structural and functional components.
Finally, in the prior art sterilization and dehumidification are attempted by two separate and distinct systems requiring heaters, fans, regulators, sensors, baffles, and other intricate bulky structural components that require servicing and frequent replacement. Heating also compromises the efficiency of the desiccant, as higher temperatures will drive water out of the desiccant as well as the object to be dehumidified or desiccated. The desiccant might be regenerated by heating, but the water must have some way to escape for this to be useful. Further, such heating has deleterious effects on the hearing aid, and the zinc air battery contained within: it is well known that heat decreases the life of most batteries, including the zinc air type.
These and other difficulties of the prior art have been overcome according to the present invention.